PROJECT SUMMARY/ABSTRACT Social communication skills lay a foundation for the development of communicative competence and healthy social relationships across the lifespan. Early-emerging and persistent social communication deficits are a hallmark feature of Autism Spectrum Disorder (ASD), and therefore a frequent target for early intervention. Unfortunately, accurate measurement of change following early intervention is currently hindered by a lack of high-quality, easy-to-use outcome measures of social communication that are suitable for very young children with ASD. To fill this gap, this R21 will focus on the development and initial validation of items for new parent- and teacher-report questionnaires for measuring social communication outcomes in 2-6 year-olds with ASD. The resulting assessment tools will be designed to measure social communication effectively across young children with ASD who have varying developmental and language levels, making them useful for tracking change as a result of early intervention. This project will follow rigorous standards for assessment development as recommended by the Food and Drug Administration (FDA) and the Patient-Reported Outcomes Measurement Information System (PROMIS), including (1) construct definition and validation via parent and teacher focus groups, expert input, and review of existing measures, (2) selection and modification of candidate items with attention to issues of construct coverage, readability, and understandability, (3) collection of preliminary data on test-retest and inter- rater reliability (n=50 each), (4) collection of preliminary data on convergent and divergent validity (n=50), and (5) examination of the factor structure of the items using data from a large group of parents (n=750) and teachers (n=400) of children with and without ASD. At the end of the project period, the investigators will have created sets of parent-report and teacher-report items (i.e., item banks) that are prepared for further refinement and validation in a future study. In particular, this item development strategy will prepare the item banks for further validation and use in a computerized adaptive testing format. Computerized adaptive tests (CATs) use item response theory (IRT) models to adaptively choose test items in real-time from a larger bank of available items, resulting in precise skill estimates with administration of fewer test items, enabling measurement that is both accurate and efficient.